H.R.H. Crown Prince Maha Vajiralongkorn (Son and the heir
apparent of King Rama IX, the current king)

H.R.H. Princess Maha Chakri Sirindhorn, the second in line
to the throne ad of December 5, 1977 since then.Her royal title in Thai language contains the word 'Crown
Princess' which is almost equivalent to her brother. But in English
language, she is styled 'Her Royal Highness' and is equivalent to the
British title of The Princess Royal.